LG Optimus Showtime (LG-L86C), suddenly cannot access router

LG Optimus Showtime (LG-L86C), suddenly cannot access router

My son's Optimus Showtime has worked flawlessly for over a year, with home wifi, hotel and other external wifi, and its 3G connection capability when wifi isn't handy.

Yesterday it suddenly stopped accessing our home wifi. When in settings, and selecting our network, it will recognize the network, secure it with WPA-2, but then display "Authentication problem." We've turned the phone on and off, turned the router on and off, done the sequence of phone off/router off/router on/phone on, all to no avail.

The 3G connectivity still works but we need to fix this and don't want to resort to a factory reset.